Weevil rescue underway

Weevil rescue underway

A
rescue mission has been mounted for a population of weevils
living on a knife edge on Wellington’s south
coast.

Department of Conservation staff and volunteers are
risking a slashing from the sharp, blade-like leaves of the
native plant speargrass to retrieve large flightless weevils
that depend on the plant for their survival. Under threat
from introduced mammals and habitat modification and in
danger of extinction, this only North Island population of
speargrass weevils (Lyperobius huttoni) is being transferred
to the safety of predator-free Mana Island.

Seven
weevils were taken to Mana Island this week as DOC
implements a plan to move up to 30 weevils from the south
coast to the island, where there is an abundance of
speargrass as well as climatic conditions which match those
on the south coast. It is hoped they will establish a
self-sustaining population there so Wellingtonians won’t
lose what is probably their most locally rare and endangered
native animal.

DOC Poneke biodiversity ranger Andrew
Morrison said most speargrass weevils were found in the
South Island, on the eastern side of the Southern Alps.

“In the North Island they are restricted to this one
small population which is also New Zealand’s only coastal
population of the species”

Speargrass (Aciphylla species)
is an alpine species, but it grows along Wellington’s south
coast and on Mana Island because the dynamic environment of
Cook Strait is similar to the alpine environment. Speargrass
weevils live and feed exclusively on the plant. The adults,
which grow up to 2 cm long, feed on the leaves and shelter
in the leaf litter under the plant, while the larvae develop
in the soil, feeding on the speargrass roots. They live for
three years, one as a larva and two years as an
adult.

“There are probably not many people aware of these
cryptic little creatures in Wellington, but they are an
important part of our biodiversity and they are threatened
with extinction,” Mr Morrison said.

“Mice and rats prey
on the weevils and wild goats and pigs destroy the
speargrass plants.”

Attempts have been made to fence off
areas of speargrass plants, kill the mice and rats with
poison baits, and replant new areas of speargrass but the
weevil population had continued to decline, he
said.

“Studies have estimated their numbers to have
dropped to around 150 individuals so it’s vital that we move
them from the vulnerable south coast location to a secure
site where their numbers can increase.”

Work will continue
to restore the south coast site so one day the weevils can
be returned to their original habitat.

Meanwhile they are
expected to thrive on Mana Island, alongside species
introduced to the island as part of a long term plan to
restore its natural ecology. Friends of Mana Island (FOMI),
which is behind the restoration project, has committed more
than $1000 in funding and volunteer support toward the
weevil transfer.

“We are pleased that yet another creature
is able to take advantage of all the work being undertaken
on Mana Island over the years to make it a safe refuge for a
variety of endangered flora and fauna,” FOMI president Brian
Paget said.

Takahe, North Island robin, brown teal, diving
petrels, fairy prion, fluttering shearwater, yellow-crowned
kakariki, speckled and spotted skinks, Wellington green
geckos and flax weevils have also been transferred to the
island. A wetland has been restored and hundreds of
thousands of native trees have been planted by volunteers.

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